Re: [PATCH] minimal SAS transport class

[Luben Tuikov <luben_tuikov@adaptec.com>]

On 08/26/05 14:48, Jeff Garzik wrote:
>>No host numbers, no routing information.  This is all
>>transparent to SCSI Core, and NONE of its business.
> 
> Routing is an essential part of the SCSI core's duties.

[I'm not a big fan of reading mixed-message emails, but what can you do...]
 
> The SCSI core is the resource manager responsible for routing messages 
> [CDBs] to/from LLDs based on <scsi-specific device address>.  This 
> includes resolution of kernel-specific identifiers (device major/minor, 
> etc.) into <s.s.d.a.>.  This also includes direct use of 

This particular is the task of sd.c.  How it does it is
sd.c. job.  Not SCSI Core.

> userspace-provided identifiers as <s.s.d.a.>, such as via SG_IO ioctl.

Ah, yes, I see.  So the question is, how do we fit SG_IO ioctl?

SG_IO can be transport/protocol agnostic _if_ SCSI Core gets
the architecture right.

I.e. if I show you a picture of the objects "out there" in the
SCSI domain, you can just point to one and send something to it.
That picture will be painted by the transport layer.  SCSI Core
is _completely_ unaware of all this!  This is how you can accomodate
SMP and any future protocols that can come your way.
 
> Moving away from HCIL requires a lot of thought, including thinking 
> about userland app breakage -- a big deal in Linux.

I never contended that userspace should be moved away from HCIL.
After all, HCIL would be just another label.

What I contend is that _internally_ SCSI Core start moving
away from HCIL and towards SAM.

Most easily this would be done by implementing a bunch of
new-way-to-do-it functions.  The request_queue wouldn't care,
and old LLDD can use the old interface, and new ones can use
the new interface.

> Ask yourself where all these HCIL-addressed CDBs come from...  each one 
> of those CDB submittors must be updated from HCIL addressing/routing to 
> transport-specific.

No, no transport specific -- I repeat again: the whole point is to move
away from "transport specific".  _SCSI_Core_can invent an HCIL label for them,
not LLDD as they currently do.

This way LLDD can be more "pure" and the gunk can go into SCSI Core, _plus_
those same LLDD can now work with the new interface.

	Luben